The present invention relates to a novel wire-driving device for a window regulator, and more particularly to a wire-driving device which can absorb automatically elongation generated in a wire for transmitting power from the wire-driving device to a working device for raising and lowering of a window glass.
Hitherto, a wire-driving type window regulator which has a wire secured to window glass and wound up or wound off to perform a slidably opening or closing action of a window glass in a building or a vehicle is well used, for changing rotational reciprocating operation of operating member into linear reciprocating motion of a window glass. Such a window regulator has some advantages, e.g. light weight and simple mechanism, due to using a wire as a transmission means. However, such a window regulator has a disadvantage in that elongation is generated in a wire in use, due to the characteristic of the wire. For that reason, elongation of the wire generates play in the rotational reciprocating operation of the driving device, so that the working device fails to accurately follow the driving device. Furthermore, elongation of the wire results in snapping of the wire due to repetitive bending of the wire, and further the wire is in danger of coming off a pulley, whereby the device becomes uncontrolable.
In order to eliminate these disadvantages, a length-adjusting member such as bolt-nut system or tension pulley system has been generally provided to the window regulator of the wire type to absorb elongation of the wire. However, in those systems, elongation of the wire must be adjusted each time there is elongation. Also, the adjustment is very troublesome, and some securing positions bring difficulties into the adjustment.
Recently, in order to eliminate these disadvantages, a transmission device capable of absorbing elongation of the wire has been suggested. This device comprises two pulleys which are provided coaxially and rotatably on a shaft and have ratchet teeth on their inner surface facing the shaft; a wire both end portions of which are respectively wound round the pulleys in an opposite direction to each other; and at least two pawls provided at the outer surface of the shaft, and respectively meshed with the above ratchet teeth. The ratchet teeth of the two pulleys are formed in the opposite direction to each other so that when the shaft is rotated in either direction, the ratchet teeth of one of pulleys are engaged with the pawl to stop the rotation of the pulley, the other pulley being freely rotatable, whereby elongation of the wire can be absorbed when the above other pulley is wound up the wire.
However, this suggested device has a problem in its strength, because the driving force is concentrated on the pawls. Therefore, the number of the pawls to be engaged with ratchet teeth must be increased. As a result, many parts are necessary in assembly of the device, and the assembly becomes very troublesome.
Also, because the device comprises two pulleys coaxially on a shaft, this device is very thick, and as a result, a wide space is required for a window regulator in a door panel of an automobile. Furthermore, to be coupled with an electric motor in a power window, the window regulator is required to be thinner.